Highways are something I never see in CAW worlds, so I decided to make a basic highway road texture with no sidewalks.
Extract the archive to Documents\Electronic Arts\The Sims 3 Create A World Tool\UserToolData\SourceTextures. The default asphalt texture is used for the road, sidewalks, crosswalks, and corners, although it shouldn't matter what texture you use for the sidewalk as the opacity map makes the sidewalk nonexistent anyway. There shouldn't be any texture clipping when you try to put the roads side by side, but I did notice some for the crosswalks.
Unfortunately, the routing is still the same, and you will have lanes that alternate in direction. I don't know if anyone has ever fixed this, but props to anyone who can because I am far too lazy.